1. Field of the Invention
The present invention relates to a method for controlling the trigger sequence in a flywheel magneto system, which system includes a magnet system for inducing a trigger pulse for a gate trigger current switch.
2. Prior art
Previously disclosed within the area of ignition circuit design is the arrangement in the primary ignition coil circuit of magneto ignition systems containing an ignition transformer of a gate trigger current switch, for example a thyristor or a transistor. These components conduct at a specific ignition time, resulting in the induction of an ignition voltage in the secondary winding of the coil. A control circuit of this kind, possibly containing a special trigger coil, is connected between the generator circuit and the control input to the gate trigger current switch. Such systems are previously disclosed, for example, through SE-B-357 032, SE-B-455 216, and SE-B-457 373. These previously disclosed systems are complicated and contain sensing devices to control the release of the trigger at an appropriate ignition time.
A flywheel magneto system of the kind mentioned above, in which the method in accordance with the invention can be applied, comprises, for example, a flywheel with a magnet unit installed in the wheel, in which two or more magnetic poles lie on an outer or inner periphery. Arranged directly adjacent to that periphery is a low-retentivity unit consisting of one or more essentially radially oriented legs. Coils are then arranged around one or more of these legs for the purpose of receiving energy from the passing magnetic poles. One common method of executing such a unit is to install all the coils belonging to the ignition system and the other electrical components in such a way that only a single core leg carries the necessary coils. Because capacitor ignition systems are concerned specifically, it is customary to utilize the most energy-rich partial wave in the induced voltage for charging the ignition capacitor. The following partial wave is used in order to initiate the ignition sequence. This permits simple and inexpensive solutions, which make effective use of the available energy. Nevertheless, the partial wave used to start the ignition sequence, "triggering", is too narrow to provide an acceptable advance of the trigger point as the speed of rotation increases, which is desirable. The form of the pulse is also influenced by the delay caused by charging of the ignition capacitor. One method of avoiding this problem is shown in the aforementioned SE-B-457 173. This procedure is less suitable, however, if the trigger-releasing coil is arranged around a core leg which is situated ahead of another core leg past which a magnetic pole moves. The reason for this is that the partial wave used in this case for a coil position of this kind is too indeterminate to produce an exact trigger point.
Another method is to utilize the last partial pulse for capacitor charging and a pulse preceding it, the middle pulse, for triggering. This gives lower energy for charging the capacitor, although in those cases in which this is acceptable, it does not produce the same disadvantages as the system described above, but rather a desired successive advance of the ignition time over the range from start-up to high speed. Unfortunately, this displacement of the ignition point reduces in proportion to the increasing diameter of the orbital path on which the magnetic poles are arranged, if the dimensions of the magnetic pole are essentially retained. The invention described below compensates for this effect.
The nature of the problems associated with the systems referred to above is that triggering at low speeds should occur at a different point on the curve than at high speeds. According to SE-B-457 286, for example, the problem is solved by connecting a computer which controls the triggering and ignition sequences. However, this previously disclosed method requires complicated and expensive components.